Fig 1.
Deformation and safety problems of the No. 1 drainage tunnel: (a) initial support, (b) secondary support.
Fig 2.
Micritic bioclastic limestone composition, as observed under a polarizing microscope.
Fig 3.
Rock specimens.
Table 1.
Specifications of MTS815.
Fig 4.
Triaxial compression test results of micritic bioclastic limestone.
Table 2.
Deviatoric stress at each level.
Fig 5.
Crack strain evolution characteristics.
Fig 6.
Moving point regression technique (after reference [43]).
Table 3.
Stress thresholds determined with different methods.
Fig 7.
Crack strain and stress thresholds of micritic bioclastic limestone.
Table 4.
Stress thresholds, stress–strength ratio Rd and characteristic axial crack strain.
Fig 8.
The rock elastic modulus results from the multilevel loading creep tests.
Fig 9.
Axial crack strain results of micritic bioclastic limestone from triaxial compression creep tests.
Fig 10.
Axial crack strain evolution of micritic bioclastic limestone under triaxial compression tests: (a) initial crack closure stage and (b) new crack growth stage.
Fig 11.
Rock crack evolution elements.
(a) Initial crack closure element, (b) New crack growth element, (c) The role of axial crack strain elements.
Fig 12.
Axial crack strain results and model fitting from triaxial compression tests of micritic bioclastic limestone.
Fig 13.
Elastic-crack model.
Fig 14.
Axial creep crack strain results of micritic bioclastic limestone from triaxial multilevel creep tests with different confining pressures.
Fig 15.
Axial creep crack strain rate of micritic bioclastic limestone from triaxial compression creep tests with 1 MPa confining pressure.
Fig 16.
Rock creep crack evolution element (Mo’s element).
Fig 17.
Axial creep crack strain results of micritic bioclastic limestone from triaxial multicreep tests and equation fitting.
Note: line stands for fitting curve, and dots stand for test data.
Table 5.
Creep crack element parameters.
Fig 18.
Creep crack element parameters.
Fig 19.
Unified transient creep constitutive model based on crack evolution.
Fig 20.
Application of the proposed constitutive models: (a) elastic-crack model, (b) transient creep unified constitutive model, (c) creep crack strain versus time and (d) creep strain versus time.